Built-up roofing has been used for many years. Built-up roofing typically utilizes a deck of wood such as plywood supported on beams or rafters. The built-up system is constructed in place and the entire roof deck is covered by a continuous weather-proof membrane usually comprising alternate layers of felt and asphalt. The membrane is applied in a field operation. Once the membrane has been applied, gravel, rock or similar aggregate is spread upon the roof to give a resistance to wear resulting from weathering and foot traffic. Typically, thermal insulation is applied at the inner side of the decking to minimize heat transfer through the deck.
Built-up systems present substantial problems where extreme temperature ranges of heat and cold are encountered. Expansion and contraction, particularly of a metal building system, can create substantial problems resulting in failure along the perimeter of the building when thermal movement is encountered.
In view of the substantial disadvantages to conventional built-up roof systems, a number of prefabricated roofing systems have been developed in the prior art. Such prior art prefabricated systems require substantial on-site construction and often do not make adequate provision for sealing around obstructions such as roof-mounted equipment and parapets. Thus, leakage can result at these points as thermal movement of the roofing system occurs. Furthermore, watertight integrity of such roofing systems is difficult to achieve and has lead to various complicated and expensive systems using sealing membranes over the expense of the roof surface.
Accordingly, there exists a need for a prefabricated system which can be quickly and easily erected with minimum labor and skill, which is reliably moisture-tight, and which is compatible with various building sizes, shapes and constructions.